Many people don’t know how different the AR-15 and AR-10 are. Despite their external and internal similarities, building an AR-10 from an 80% lower is quite different in a mechanical context, yet the machining methods are quite similar. There is one primary reason for this. Nearly all AR-15 parts are now considered mil-spec. This is a measurement system that ensures all parts work together regardless of maker, as they are all created from the same molds and manufacturing methods. The one part of an AR-15 that isn’t always mil-spec is the buffer tube, which is either commercial or mil-spec. Outside...